Mike's Workshop Notebook

Center Plate Bolser

This center plate is part of a redesigned leading truck for a Little Engines Northern 4-8-4 locomotive. The original configuration had a notable drawback: the leading truck was not positively attached to the locomotive frame. In the event of a derailment, this allowed the truck to separate completely from the engine.

Reinstalling the truck under an approximately 1,100 lb locomotive—while also aligning the heart rockers—would be a challenging and impractical task in the field.

The redesign addresses this issue by incorporating a positive attachment between the leading truck and the locomotive frame. This ensures the truck remains properly located, even in the event of a derailment.

This casting introduced the added challenge of making and using a core as part of the process. A core is used to create internal voids within a casting—areas where metal is not desired—allowing for more complex internal geometry that cannot be formed by the mold alone.

Photos

Leading Truck Pattern — These are the cope and drag patterns used for the mold. A key feature is the cylindrical projection located at the center of the cope pattern. This forms a matching circular recess in the cope sand during molding. That recess serves an important purpose—it acts as a core print, providing a positive locating and support point for the core that forms the central hole in the casting.

The core produces the internal bore of the center plate. It was made using a 3D-printed mold, packed with a mixture of fine sand and sodium silicate binder. Once packed, the mold assembly was placed in a sealed plastic bag and exposed to carbon dioxide gas. The CO₂ reacts with the sodium silicate, curing and hardening the sand into a rigid, self-supporting core.

After the core was prepared, the external mold was formed in the usual way using the cope and drag. The hardened core was then carefully positioned in the mold cavity, the mold assembled, and the setup prepared for pouring.

Leading Truck Pic — The casting after mold breakout and initial cleanup, ready for machining. At this stage, the gates and any remaining flash has been removed.
The large central bore—formed by the core—is clearly visible. Its clean formation and alignment are a good indication that the core was properly positioned and supported during the pour.